I have removed one compensation or ball screw from a Lefever 20. It measures .522" (no taper apparent) and 22 threads per inch. It is a slotted screw and came out easily...which I did not expect. I only tried that because the frame was to be annealed for engraving and didn't wish to mess with the temper of the screw.. Fortunately I had the forethought to apply witness marks so the screw will go back in to the same depth. The threads in the frame are like Miller mentioned, tapered on the inside end which I assume is from the tap?

Sam Welch